Method of modifying the rate of temperature change of an epoxy resin composition in a resin container during a casting process

ABSTRACT

A method for modifying a rate of temperature change of an epoxy resin composition in a resin container during a resin casting process is proposed. The resin composition has at least one epoxy monomer component and a curing agent. A passivation agent for the curing agent is added to the epoxy resin composition. A resin container arrangement for use in such a resin transfer moulding process, a composite product having an epoxy resin composition, and a use of an organic acid in an epoxy resin casting process as a passivation agent for modifying the rate of temperature change in a resin container containing an epoxy resin composition are proposed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims priority to U.S.application Ser. No. 13/951,503, filed Jul. 26, 2013, which claimedpriority to European Patent Office application No. 12179634.6 EP filedAug. 8, 2012, the entirety of each of these references is herebyincorporated by reference herein.

FIELD OF INVENTION

The invention relates to a method of modifying the rate of temperaturechange and preferably of lowering the temperature of an epoxy resincomposition in a resin container during a resin casting process,especially a resin infusion or a resin transfer moulding (RTM) process,a resin container arrangement for the use in such a resin transfermoulding process, a composite product comprising an epoxy resincomposition, and a passivation agent in an epoxy resin casting process.

BACKGROUND OF INVENTION

WO 2009103736 describes a vacuum infusion or vacuum assisted resintransfer moulding process (VARTM) process used for moulding fibrecomposite mouldings. In such a process uniformly distributed fibres arelayered in a first mould part, the fibres being rovings, i.e. bundles offibre bands, bands of rovings or mats, which are either felt mats madeof individual fibres or woven mats made of fibre rovings. A second mouldpart, which is often made of a resilient vacuum bag, is subsequentlyplaced on top of the fibre material. By generating a vacuum in the mouldcavity between the inner side of the first mould part and the vacuumbag, the liquid resin can is drawn in and fill the mould cavity with thefibre material contained in the mould. So-called distribution layers ordistribution tubes are used between the vacuum bag and the fibrematerial in order to obtain as sound and efficient distribution of resinas possible. In most cases the resin applied is polyester, vinyl esteror epoxy, and the fibre reinforcement is most often based on glassfibres or carbon fibres, but may also be plastic fibres, plant fibres ormetal fibres.

The liquid resin is provided in a resin container, also called mixingbucket, filled with a resin/curing agent composition prepared in amixing unit, adapted for mixing the resin monomer components and thecuring agent in the respective amounts. As the curing reaction hasalready been started in the mixing unit, the exothermic polymerisationcontinuously raises the temperature in the resin container.

During the process of filling the mould, a vacuum, i. e. anunder-pressure or negative pressure, is generated in the mould cavity,whereby liquid resin is drawn from the resin container or mixing bucketinto the mould cavity via the inlet channels in order to fill said mouldcavity. From the inlet channels the resin disperses in all directions inthe mould cavity due to the negative pressure as a flow front movestowards the vacuum openings for generating vacuum inside the mould.

In the resin container such as the mixing buckets or the overflowcontainer in such casting processes, e. g. blade casting methods forwind rotor blades, no solution exists for preventing the ignition offire during the curing process which is caused by the exothermicreaction between the epoxy resin monomers and the curing agent.Conventionally, the mixing bucket is moved outdoors if signs of fireignition or smoke development are observed in the mixing bucket to avoidany damages of the casting apparatus or the casting facilities and toprotect the working environment of the staff around the blade mould.

U.S. Pat. No. 5,721,323 describes a prepreg containing a resincomposition consisting of a polyepoxide, a curing agent, a catalyst forthe reaction of the polyepoxide with the curing agent and a Lewis acidcure inhibitor for inhibiting the catalyst by means of forming acatalyst Lewis acid inhibitor complex. Cured and partially cured epoxyresins are used in coatings or laminates, wherein the inhibitor is usedfor inhibiting the curing reaction of polyepoxide by forming a stablecomplex between the curing agent and the Lewis acid in the prepreg andreleasing the catalyst if a predetermined temperature level has beenreached during the curing process. This inhibiting method is used forstoring the polyepoxide resin composition in prepregs which are thenused in moulding processes of composite parts. However, these prepregsare not used in casting process such as rein transfer mouldingprocesses.

SUMMARY OF INVENTION

It is an object of the present invention to improve the safety ofcasting processes, in particular to prevent the ignition of fire in amixing bucket during a casting process like a resin infusion or resintransfer moulding process, and to provide composite products in a safeand economic manner.

The object of the invention is achieved by a method of modifying therate of temperature change of an epoxy resin composition in a resincontainer during a resin casting process, a resin container arrangementfor the use in such a resin transfer moulding process, a compositeproduct comprising an epoxy resin composition, and the use of an organicacid in an epoxy resin casting process according to the claims.

The method of modifying or changing the rate of temperature change of anepoxy resin composition in a resin container, that means in the resinfilled system, during a resin casting process according to a firstaspect of the invention comprises the step of adding a passivation agentfor the curing agent to the epoxy resin composition. The resincomposition comprises at least one epoxy monomer component and a curingagent. A passivation agent as understood in the following description ofthe invention inhibits the polymerization reaction and is advantageouslya curing agent reactive component, which causes a modification of therate of temperature change and especially a lowering of the reactiontemperature during the reaction with the curing agent. Especially, thepassivation agent, as used according to the invention, does not cause apassivation of the surface of any reaction component, but changes thetotal reaction temperature or enthalpy of all reactions taking place inthe resin mixture. More particularly, the passivation reaction is not aninhibition of the polymerization reaction by means of lowering thereaction rate, but reduces the amount of free curing agent by thepassivation agent, while generating less heat in this reaction as willbe generated by the polymerisation reaction. Hence, the reactionenthalpy can be reduced by adding a passivation agent into the curingreaction. In addition or alternatively, the time of generating reactionheat can be prolonged by the addition of the passivation agent.

The ignition of a fire in a mixing bucket in which the polymerisationreaction takes place can advantageously prevented by modifying the rateof temperature change or inhibiting the increase of the temperature ofthe reactions between the catalyst and the epoxy monomers and thecatalyst and the passivation agent which are generally exothermicreactions.

Thus, the modification of the rate of temperature change of theexothermic polymerisation reaction by means of the addition of apassivation agent into the resin composition usually allows a saferprocessing. In particular, the step of potentially moving the mixingbuckets out of the factory site in case first signs of fire ignition orsmoke are observed in the mixing bucket can be omitted. Hence, a saferand more reliable casting process has been developed.

A resin container arrangement according to a second aspect of theinvention is adapted for the use in a resin transfer moulding process.The arrangement can be an integrally provided system or a system withseparated means which can be combined to the total arrangement or can bea part of a casting apparatus. The arrangement comprises at least amixing bucket and a passivation agent container, which are preferablyfluently connected with each other in order to can add the passivationagent into the mixing bucket. The resin container arrangement is usedfor mixing an epoxy resin composition comprising at least one epoxyresin monomer component and a curing agent with a passivation agent inthe mixing bucket in order to achieve the effects described in the firstaspect of the invention.

According to a third aspect of the invention, a composite product,preferably being prepared according to the method of the first aspect,comprises an epoxy resin composition or is based on an epoxy resincomposition, generally containing 50 wt-% of epoxy resin or even more.The composite product comprises a passivation agent or a reactionproduct of a passivation agent and a curing agent. The product differsfrom conventional products in an amount of passivation agent or itsreaction product obtained by the passivation reaction. The amounts canbe 1 to 20 wt-%, preferably 1 to 10 wt-%, more preferably lower than 5wt-%. Depending on the curing rate and the temperature within the mixingcontainer, the free organic acid or any reaction product with the curingagent may be present in the finished product. Thus, it is easy todetermine whether or not the product has been obtained by using anorganic acid during the manufacturing method of the composite products.The products may have fewer defects due to high temperatures inside themould during the casting process and, thus, are advantageous over theconventional products, especially are more reliable.

The epoxy resin composition used in such a method, resin containerarrangement, or product comprises, according to another aspect of theinvention, at least one epoxy resin monomer component, a curing agentand a passivation agent. This epoxy resin composition can advantageouslyused in a resin infusion or RTM process, for example for manufacturingblades for wind rotors. The epoxy resin composition preferably modifiesthe rate of temperature change or even lowers the temperature in a resincontainer used for mixing a resin monomer component with a curing agent.The passivation agent inhibits the increase of the temperature orreduces the total reaction temperature and, thus, prevents the resinmixture from ignition of a fire.

According to a further aspect of the invention, the application refersto the use of an organic acid in an epoxy resin casting process,preferably a resin infusion or resin transfer moulding process (RTM).The organic acid is added to a resin container, e.g. a resin filledsystem part such as the mixing bucket or resin overflow container, inorder to keep the temperature level at a predefined maximum temperatureby means of lowering the rate of the temperature increase by means ofpassivation an amount of the curing agent with the passivation agent.Thereby, the passivation reaction preferably elongates the time forraising the temperature in the resin container. Alternatively, thepassivation reaction substantially keeps constant or lowers thetemperature of the resin mixture contained therein. This canadvantageously initiated by means of a reaction between the curing agentand the passivation agent as defined with regard to the first aspect ofthe invention. Keeping the temperature “substantially constant” meansthe temperature rising rate is very small or preferably nearly zero.

Particularly advantageous embodiments and features of the invention forimproving, for example, the safety of such casting processes or makingthe processes more cost effective, are given by the dependent claims, asrevealed in the following description. Further embodiments may bederived by combining the features of the various embodiments describedin the following, and features of the various aspects and/or claimcategories can be combined in any appropriate manner.

In a preferred embodiment of the method according to the invention, thecuring agent comprises an amine-based curing agent because those curingagents are stable and cheap. Preferred examples are primary (R—NH₂) orsecondary (R—NH—R′) amines. Amines generally have reactive sites forreacting with the epoxy groups of the epoxy resin monomers in a step(growth) polymerization reaction by generating epoxy-amine reactionproducts which can be combined to each other forming oligomers orpolymers. Additionally, chain reactions or side reactions like formingside chains can take place. Exemplified amine-based curing agents can bealiphatic, cycloaliphatic or aromatic amines.

The passivation agent used in a preferred embodiment according to theinvention may comprise an organic acid which can more preferably form asalt with the curing agent. More preferably, the organic acid is ahydrophilic organic acid comprising more than one hydrophilic group.Advantageously, divalent or trivalent organic acids, that means organicacids with at least two carboxyl groups such as citric acid or malicacid (e. g. two, three, or more carboxyl groups) can be used. Thedivalent or trivalent organic acids are preferred because breaking thehydrogen bonds or interactions between two carboxyl groups is anendothermic process which reduces the total reaction temperature (thefree enthalpy) of the passivation agent modified curing process. Afterdissolution of the organic acid in resin mixture, the acid undergoes anexothermic reaction with the amine groups in the curing agent. Theorganic acid is chosen in such a manner that the enthalpy of thedissolution and the enthalpy of the amine reaction are of similar size.More preferably, the enthalpy of the dissolution exceeds that of thereaction between the amine and the organic acid. By reacting with theorganic acid, the amine groups become unavailable for the exothermicreaction with the epoxy groups. Owing to the lower availability of aminegroups, the temperature increase during the curing process of the epoxyis suppressed. Thereby, the rate of the rise of the temperature in theresin container can be slowed down. That means the rate of thetemperature change, or the temperature generated in the resin containerover the curing time can be lowered in the mixing container bypassivation of a part of the curing agent.

The curing reaction, i. e. the polymerization reaction and especiallythe rate of the polymerization reaction, is not significantly affected.The amount of the curing agent is reduced and, thus, the addition of thepassivation agent mainly reduces the curing extent which can for examplebe measured by determining the glass transition temperature of the curedresin mixture.

Alternatively, the passivation of the curing agent by the passivationagent may also be reversible. Then, the curing reaction is temporarilyinhibited and the resin can be cured in its full extent after thetemporary passivation has been removed This can for example be done ifthe formed salt is unstable at larger temperatures, i.e., the saltdissolves after the reaction heat of the polymerization reactiongenerated sufficient heat to liberate the amine groups. Furthermore, itis preferred that the acid evaporates after liberation from the saltduring the curing reaction or is embedded in the cured epoxy. Anincorporation or the acid into the cured epoxy can lower the strength ofthe cured epoxy resin.

A further preferred embodiment of the method according to the inventionuses an organic acid comprising one or more hydrophilic substituents atits backbone. Preferred hydrophilic groups are additional carboxylicgroups or hydroxyl groups. If more hydrophilic groups are present theenthalpy of dissolution of the passivation agent in the resin mixture ismore positive and, thus, the increase in temperature of the totalreaction is smaller or the temperature is even lowered to some extent inthe resin container during the curing reaction.

The epoxy resin composition used in a further embodiment of the methodaccording to the invention comprises the epoxy resin monomer componentin an amount of 100 parts per weight and a curing agent in an amount ofabout 10 to 40 parts per weight, preferably more than 20 and less than30 parts per weight, more preferably between 25 and 28 parts per weight.Advantageously, the passivation agent is contained in this compositionin an amount sufficient for at least partly reacting with the curingagent and sufficient to lower the temperature of the resin composition,more preferably in a molar amount of about 2 to 30 parts per mole, morepreferably about 5 to 20 parts per mole and in particular about 10 partsper mole of curing agent, for example of the molar amount of reactiveamine groups.

According to a preferred embodiment of the method according to theinvention, the passivation agent is added to the resin container in astep of curing a resin composition of a resin infusion or resin transfermoulding (RTM) process. Preferably the resin composition comprisesexcess resin not used for casting a product which is for example kept inthe resin system such as the resin mixing bucket or the resin overflowcontainer but also in the respective connections between the respectivesystem parts such as lines. Preferred resin containers into which thepassivation agent can be added, are the mixing bucket or overflowcontainer in an RTM process, especially in a VARTM process.

It is preferred that the method according to a preferred embodimentcomprises the step of adding the passivation agent in the form of asolution into the resin container. The solution can be prepared directlybefore the addition. Alternatively, the passivation agent can be storedin the form of a solution. Especially if the passivation agent is solidat room temperature, it is preferred to dissolve it into a suitablesolvent, preferably a solvent which is already used in the resincomposition or the reaction mixture. Of course, if the passivation agentis in solid or liquid (pure or dissolved in a solvent) form at roomtemperature, the direct addition in the respective form is likewisepossible. After the addition of the solid passivation agents or thepassivation agents in liquid or dissolved form, the resin mixturepreferably is stirred by a stirrer in the resin container to dissolvethe passivation agent in the resin mixture.

The method is preferably used for casting processes such as RTMprocesses in the field of manufacturing blades, for example wind rotorblades. However, it can be used in the field of automobile production ora similar field of engineering, in which high amounts, that means up toseveral kilograms, for example 1 to 10.000 kg, preferably, 10 to 5.000kg, of mixed resin compositions are prepared in resin containers such asmixing buckets. Especially in these fields it is demanded to lower thetemperature or at least the rate of temperature rise of the resinmixtures to be cured in the resin containers to improve the workingenvironment of the workers in relation to safety and in order to reducethe risk of fire inside the production sites at the factories.

The use of an organic acid in an epoxy resin casting process as apassivation agent for modifying the rate of temperature change in aresin container containing an epoxy resin composition comprising atleast one epoxy monomer component and a curing agent is therefore arelative economic solution and can easily be implemented in or added toconventional processes. More particularly, the reaction heat or theenergy release during the polymerisation reaction is lowered, at leastto some extent, or is generated over a larger reaction time. Therefore,the resin container according to the second aspect or the use of anorganic acid according to the third aspect of the invention in a castingprocess such as a RTM process has the same advantages as described withregard to the method according to the invention. Thereby, thetemperature of the resin contained in the resin container arrangementcan be manually or automatically controlled to a temperature below theignition point, preferably below about 250° C., and more preferablybelow about 190° C. In case of resin amounts below 2 kg, for example inamounts of between 0.2 kg to 1.5 kg, preferred upper temperature limitsare about 160° C., more preferably about 150° C., 140° C., 130° C., 120°C., 110° C. or lower.

It is preferred that the resin container is a resin mixing bucket or aresin overflow container. According to a preferred embodiment, theorganic acid can, thus, be used for preventing ignition of fire in amixing bucket or resin overflow container of a resin infusion or a resintransfer moulding process. Such containers can contain about 1 to 501 ofmixed epoxy resin. The larger the epoxy resin amount contained thereinthe larger is the risk of ignition.

According to a preferred embodiment of the composite product accordingto the invention, the passivation agent or the reaction product iscontained in the form of an organic acid, an ammonium carboxylate saltof an organic acid and an amine-based curing agent, an amide productbetween an organic acid and an amine-based curing agent or a mixture ofthem. Depending on the temperature during the casting process, the endproduct may contain either the free organic acid to some extent or areaction product of the free acid and the curing agent, especially anamine-based curing agent. In this case, the first step of thepassivation reaction can be the formation of an amine salt between theorganic acid and the amine-based curing agent. At a temperature of 100°C. or higher, the ammonium carboxylate salt may be transformed into anamide consisting of the residues of the original acid and amine. Thus,depending on the temperature within the resin mixture, the free organicacid, the ammonium carboxylate salt or the amide may be contained aloneor in a mixture of two or three of these components.

The composite product prepared by the method of the present invention orprepared by using an organic acid during the casting process can be awing or blade, in particular for wind rotors, or a car part. As fewerdefects are present within the composite product, those products areadvantageous over the conventionally prepared products.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawing. It is to be understood, however, that thedrawing is designed solely for the purpose of illustration and not as adefinition of the limits of the invention.

FIG. 1 shows a schematic cross-sectional view of an RTM apparatuscomprising a passivation agent container,

FIG. 2 shows a temperature vs. time plot of the experimental resultsobtained in Examples 1 and 2,

FIG. 3 shows a temperature vs. time plot of the experimental resultsobtained in Examples 3 and 4.

DETAILED DESCRIPTION OF INVENTION

The FIG. 1 shows an RTM apparatus with a pure resin container A, a purehardener or curing agent container B, a mixing unit C, a mixing bucketD, a blade mould E and an overflow container F for excess resin.Moreover, a passivation agent container G and a passivation agent inletH are provided and connected with the mixing bucket D.

The RTM process is generally done by mixing the pure resin (an epoxyresin) and the pure hardener (an amine) in the mixing unit c and pouringthe resin/hardener mixture into the mixing bucket D. The resin/hardenermixture is then used for casting the blade in the blade mould E by meansof vacuum assisted resin transfer moulding. After the moulding of theblade in the blade mould, the excess resin is collected in the resinoverflow container F and disposed after the resin mixture is hardened.Of course other casting processes can be used as well and also fallwithin the scope of the present invention.

In the mixing bucket E, the temperature raises because of the exothermicpolymerization reaction of the epoxide monomers with the amine curingagent. In order to keep the temperature in the mixing bucket D within apredetermined temperature range, the temperature is controlled and, ifnecessary, an organic acid is added from the passivation agent containerG via the passivation agent inlet H. The addition of the passivationagent can be controlled by means of a manual or automatic control means(not shown) which can receive temperature measuring signals from thetemperature sensor inside the mixing bucket D. Thereby, the temperaturecan be controlled within a level in order to prevent fire ignitioninside the mixing bucket D during or after the casting process,preferably to keep the temperature below 250° C.

FIG. 2 shows a temperature vs. time plot of the experimental resultsobtained with the organic acids ethanoic acid and octanoic acid inexamples 1 and 2 compared to a reference sample. The monovalent acidsboth show a faster increase of the temperature than the referencesample. Moreover, the maximum temperature in the resin container ishigher or similar to that of the reference sample.

FIG. 2 shows a temperature vs. time plot of the experimental resultsobtained with malic acid and citric acid in examples 3 and 4 compared toa reference sample. The samples containing organic acids having morethan one carboxylic acid group, such as two in malic acid and three incitric acid, respectively, show a significantly reduced maximumtemperature of about 90 to 110° C., and a slow temperature increase thanthe reference sample. Details will be explained in the followingdescription of the examples.

Examples 1 to 4

General experimental procedure:

The experiments were carried out with the industrially available epoxysystem from Momentive, RIM035/RIMH038. The RIM035 resin is based on atleast 90 wt-% diglycidylether of bisphenol A (DGEBA) and less than 10wt-% of C12 and C14 monooxiranes. The RIMH038 curing agent contains50-70 wt-% polyoxypropylenediamine. The resin and the curing agent wereprior to experiments preheated to 25° C. 587.3 g of RIM035 resin wasmixed with 162.7 g RIMH038 curing agent (stoichiometric ratio). Thecuring agent and the resin were manually mixed with a wooden spatula for4 minutes in a mixing bucket. After mixing the curing agent and theresin, the organic acid was added to the mixture in a molar ratio of1/16 with respect to the curing agent content. The added organic acidshad room temperature. After adding the acid, the mixture was stirredagain. A J-type temperature sensor was placed in the centre of themixing bucket containing the resin, curing agent and organic acid andthe mixing bucket was placed in a Friocell heating chamber (MMMMedcenter Einrichtungen, Germany) operating at 25° C. The temperature inthe mixture was measured every minute throughout the curing process.

The following organic acids have been used in the Examples 1 to 4 (allacids have been obtained from Sigma-Aldrich):

Example 1

acetic acid (purity ≧99% LOT SHBB1567V), also called ethanoic acid

Example 2

octanoic acid (purity ≧98% LOT STBC3482V)

Example 3

DL-malic acid (purity ≧98% LOT SLBB6897V)

Example 4

citric acid (99% purity, LOT 091M0211V)

The reference sample shown in the FIGS. 2 and 3 is the same resinmixture without the use of any passivation agent.

In FIG. 2, the graphs represent the temperature measured in the mixingbucket every minute for the two organic acids ethanoic acid and octanoicacid and the reference sample. As the two organic acids are liquid atroom temperature, they were added into the mixing bucket in liquid form.From FIG. 2 it can be gathered that the resin mixture containingethanoic acid shows a strong increase of the temperature after about 50minutes while the maximum temperature was about 180° C. (at about 70 to130 minutes). The corresponding octanoic acid sample shows a significanttemperature increase at about 100 minutes after the addition of theorganic acid, while the maximum temperature was about 220° C.

FIG. 3 shows the respective graphs for the resin samples containingmalic acid and citric acid, respectively, compared to the graph of thereference sample. The two organic acids are solid at room temperatureand, thus, were added in the solid form. The resin mixture cured underheat generation by the exothermic polymerisation reaction. The maximumtemperature was about 90° C. and about 110° C. for malic acid and citricacid, respectively. The maximum temperature in the mixing bucket wassignificantly lower in the samples with the organic acids compared tothe temperature measured in the reference sample. The maximumtemperature peak was measured after about 350 and 400 minutes,respectively. Therefore, the Examples 3 and 4 show that the hydrophilicorganic acids having two or three carboxylic groups slow down theincrease in temperature of the resin mixture during the polymerizationreaction because of passivation of parts of the curing agent by theorganic acid.

Example 5 Temperature Increase

To clarify the different role of hydrophobic acids (ethanoic andoctanoic acid) and hydrophilic acids (citric and malic acid), thetemperature immediately after mixing was measured. The experimentalsetup was similar to the one described in the Examples 1 to 4 and themolar ratio of acid was 1/16 with respect to the curing agent. Thetemperature increase was determined as the difference between thehighest obtained temperature within the first 5 minutes after theaddition of the organic acid and the temperature prior to the additionof the organic acid.

These were the results:

Citric acid 0.3° C.DL-malic acid 0.4° C.Ethanoic acid 6.2° C.Octanoic acid 7.6° C.

In the light of the above results, it has been shown that organic acidscapable of lowering the peak temperature during curing display atemperature increase below 1° C. in the first 5 minutes after theaddition of the organic acid. That means, organic acids capable oflimiting the temperature increase in the first minutes to a maximumchange of about 1° C., such as the solid and/or hydrophilic organicacids having more than one carboxylic groups are preferred in the use aspassivation agent. The reason may be the endothermic breakage of thehydrogen bonds in the hydrophilic organic acid, for example between thetwo or more carboxylic groups. Otherwise the dissolution enthalpynecessary for dissolving the solid organic acids in the resin mixturemay be responsible for the advantageous results of the malic and citricacid.

Although the present invention has been disclosed in the form ofpreferred embodiments and variations thereon, it will be understood thatnumerous additional modifications and variations could be made theretowithout departing from the scope of the invention. While the inventionhas been described with reference to RTM processes for manufacturingwind turbine blades, other resin composite materials such as wings orrotors for airplanes, helicopters, coolers, or car parts as well asparts in the automotive industry or similar devices may also be preparedwith the method of the invention. An organic acid as passivation agentscan generally be used in the field of casting processes or resintransfer moulding processes, e.g. in vacuum assisted resin transfermoulded processes etc. For example, the organic acid can be used forautomatically controlling the temperature in resin containers used incasting processes. For the sake of clarity, it is to be understood thatthe use of “a” or “an” throughout this application does not exclude aplurality, and “comprising” does not exclude other steps or elements. A“container”, “unit”, “means” or “device” can comprise a number ofseparate containers, units, means or devices, unless otherwise stated.

1. A mixture comprising: an epoxy resin monomer component comprisingepoxy monomers; a curing agent effective to react with the epoxymonomers via an exothermic polymerization reaction; and a passivationagent effective to modify a rate of temperature change of or inhibit anincrease of temperature from the polymerization reaction.
 2. The mixtureof claim 1, wherein the passivation agent comprises an organic acid. 3.The mixture of claim 2, wherein the organic acid comprises two or morecarboxylic acid groups.
 4. The mixture of claim 2, wherein the organicacid comprises one or more hydrophilic constituents.
 5. The mixture ofclaim 2, wherein an enthalpy of the dissolution of the organic acid inthe mixture is greater than an enthalpy of a reaction between the curingagent and the passivation agent.
 6. The mixture of claim 2, wherein theorganic acid is selected from the group consisting of malic acid andcitric acid.
 7. The mixture of claim 1, wherein the curing agentcomprises an amine-based curing agent.
 8. The mixture of claim 1,wherein the curing agent comprises about 10 to 40 parts per weight andthe passivation agent comprises about 2 to 30 parts per mole of thecuring agent.
 9. The mixture of claim 1, wherein the epoxy resin monomercomponent is present in an amount of 100 parts per weight.
 10. A resincontainer arrangement comprising: a first vessel comprising a mixture ofan epoxy resin monomer component comprising epoxy monomers and a curingagent; a second vessel comprising an amount of a passivation agent influid connection with the first vessel; and means for adding thepassivation agent from the second vessel to the first vessel to modify arate of temperature change of or inhibit an increase of temperature froma polymerization reaction in the first vessel between the epoxy monomersand the curing agent.
 11. The arrangement of claim 10, wherein thepassivation agent comprises an organic acid.
 12. The arrangement ofclaim 11, wherein the organic acid comprises two or more carboxylic acidgroups.
 13. The arrangement of claim 11, wherein the organic acid isselected from the group consisting of malic acid and citric acid. 14.The arrangement of claim 10, wherein the curing agent comprises anamine-based curing agent.
 15. The arrangement of claim 10, wherein thecuring agent is present in an amount of about 10 to 40 parts per weightand the passivation agent is in an amount of about 2 to 30 parts permole of the curing agent.
 16. The arrangement of claim 10, wherein theepoxy resin monomer component is present in an amount of 100 parts perweight.
 17. A composite product, comprising: a polymerized epoxy resincomprising a reaction product of an organic acid and an amine-basedcuring agent, wherein the reaction product comprises a salt of theorganic acid and the amine-based curing agent, an amide product betweenthe organic acid and the amine-based curing agent, or a mixture thereof.18. The composite product of claim 17, wherein the composite productcomprises a wind turbine blade.
 19. The arrangement of claim 10, whereinthe organic acid comprises two or more carboxylic acid groups.